System and method for delivering a target volume of fluid

ABSTRACT

A method for delivering a target volume of fluid to a destination is provided. The method includes delivering a first volume of fluid to the destination in increments each having approximately a first incremental volume, the first volume of fluid being less than the target volume and delivering a second volume of fluid to the destination in increments each having approximately a second incremental volume, the second incremental volume being less than the first incremental volume, such that the sum of the first volume and the second volume is approximately equal to the target volume.

[0001] The present application claims priority from U.S. ProvisionalApplication Serial No. 60/371,894 which is hereby incorporated herein byreference.

TECHNICAL FIELD AND BACKGROUND ART

[0002] The present invention relates to fluid delivery systems, and inparticular to systems and methods for accurately delivering a targetvolume of fluid to a destination.

[0003] Such systems regulate the rate of flow of fluid through a line.Some examples of fluid delivery systems are peritoneal dialysis machinesand intravenous fluid delivery systems. These systems may include apermanent housing which does not come into direct contact with thetransporting fluid and into which a fluid-exposed disposable cassette isplaced. The disposable cassette includes flexible membranes, or otherstructures that respond to pressure and that separate the permanentcomponents from the fluid being delivered. Examples of such fluiddelivery systems and their sub-components (e.g., pressure conductionchambers, flow measurement systems and valves) are disclosed in U.S.Pat. Nos. 4,778,451, 4,826,482, 4,976,162, 5,088,515, 5,178,182 issuedto Kamen, U.S. Pat. No. 5,989,423 issued to Kamen et al. and U.S. Pat.No. 6,503,062 issued to Gray et al. These patents are all herebyincorporated herein by reference.

[0004] One problem with respect to fluid delivery systems, such as inperitoneal dialysis, arises when treating subjects with low fill volumecapacities, such as a child. For example, in peritoneal dialysissystems, a fill volume of 1000 mL or less generally indicates a low fillvolume while fill volumes of greater than 1000 mL are typical for anaverage adult's fill volume. Thus, a single fluid delivery system maynot be appropriate for treating both an average adult and a child.

[0005] Another problem arises with respect to fluid delivery systemswhen two or more fluids from two or more sources must be delivered to asubject or patient simultaneously and in a particular ratio. It isdifficult to maintain a consistent ratio of the different fluids forsimultaneous delivery to the subject because each source may deliver itssolution to the system at different rates and/or in different volumes.Consequently, it is difficult to maintain a consistent ratio of thedifferent fluids in the fluid delivery system at any one time.

SUMMARY OF THE INVENTION

[0006] In a first embodiment of the invention, a method for delivering atarget volume of fluid to a destination includes delivering a firstvolume of fluid to the destination in increments each havingapproximately a first incremental volume, the first volume of fluidbeing less than the target volume. A second volume of fluid is thendelivered to the destination in increments each having approximately asecond incremental volume. The second incremental volume is less thanthe first incremental volume, and the sum of the first volume and thesecond volume is approximately equal to the target volume. Deliveringthe first and second volumes of fluid to a destination may includedelivering the first and second volumes of fluid parenterally to a humansubject. Similarly, delivering the first and second volumes of fluid toa destination may include delivering the first and second volumes offluid to a fluid reservoir and/or delivering the first and secondvolumes of fluid to a container. Such a container may be a heating bag,such as may be used in conjunction with a peritoneal dialysis system,and/or a pump chamber. In accordance with a related embodiment, thefirst volume may be approximately equal to the target volume minus afinish volume and the second incremental volume may be less than thefinish volume. In a related embodiment, the second incremental volumemay be less than one third the finish volume.

[0007] In accordance with another embodiment of the invention, a systemfor delivering a target volume of fluid to a destination includes afluid control module for delivering a first volume of fluid to thedestination in increments each having approximately a first incrementalvolume, the first volume of fluid being less than the target volume. Thefluid control module also delivers a second volume of fluid to thedestination in increments each having approximately a second incrementalvolume, the second incremental volume being less than the firstincremental volume. The sum of the first volume and the second volume isapproximately equal to the target volume. The system also includes avalve arrangement for controlling fluid communication to the destinationand a controller for determining the volume of fluid delivered to thedestination and for controlling the valve arrangement and the fluidcontrol module. The fluid control module may deliver the first andsecond volumes of fluid to a human subject and the first and secondvolumes of fluid may be delivered parenterally. Similarly, the fluidcontrol module may deliver the first and second volumes of fluid to afluid reservoir and/or a container such as a heating bag and/or a pumpchamber.

[0008] In accordance with related embodiments, the first volume may beapproximately equal to the target volume minus a finish volume and thesecond incremental volume may be less than the finish volume. Forexample, the second incremental volume may be less than one third thefinish volume.

[0009] In accordance with a further embodiment of the invention, amethod for simultaneously delivering a target volume of fluid from twosources in a desired ratio to a common destination includes delivering afirst volume of fluid from a first source and a second volume of fluidfrom a second source to the destination in increments each havingapproximately a first incremental volume, the first incremental volumeof fluid being substantially less than the target volume. After deliveryof a first incremental volume of fluid from the first source and thesecond source, the volume of fluid delivered to the destination from thefirst source and the volume of fluid delivered to the destination fromthe second source is measured. Delivery of the first volume of fluid tothe destination is suspended when the first volume exceeds the secondvolume by a fraction, which may be a predetermined fraction, of thefirst incremental volume. A first incremental volume of fluid from thesecond source is delivered to the destination, and delivery of the firstvolume of fluid to the destination is resumed.

[0010] In accordance with related embodiments, the first incrementalvolume of fluid may be less than one quarter of the target volume. Inaccordance with further related embodiments, the desired ration may be1:1 and the predetermined fraction may be one half. Delivering the firstand second volumes of fluid to a destination may include delivering thefirst and second volumes of fluid parenterally to a human subject.Similarly, delivering the first volume and second volumes of fluid to adestination may include delivering the first and second volumes of fluidto a fluid reservoir and/or container, and such a container may be aheating bag and/or a pump chamber.

[0011] In accordance with other related embodiments, the method mayinclude determining that approximately the target volume of fluid hasbeen delivered to the destination and measuring the volume of fluiddelivered to the destination from the first source and the volume offluid delivered to the destination from the second source. A thirdvolume of fluid from the source that has delivered a smaller volume offluid to the destination may then be delivered in increments each havingapproximately a second incremental volume, the second incremental volumebeing less than the first incremental volume, such that the volume offluid delivered to the destination from the first source and the volumeof fluid delivered from the second source are in approximately thedesired ratio. The sum of the first volume and the second volume may beapproximately equal to the target volume minus a finish volume, and thesecond incremental volume may be less than the finish volume. In onerelated embodiment, the second incremental volume is less than one thirdthe finish volume.

[0012] In accordance with another embodiment of the invention, a systemfor simultaneously delivering a target volume of fluid from two sourcesin a desired ratio to a common destination includes a first fluidsource, a second fluid source, and a fluid control module. The fluidcontrol module delivers a first volume of fluid from the first fluidsource and a second volume of fluid from the second fluid source to thedestination in increments each having approximately a first incrementalvolume, the first incremental volume being substantially less than thetarget volume. The fluid control module also measures the volume offluid delivered to the destination from the first source and the volumeof fluid delivered to the destination from the second source, suspendsdelivery of the first volume of fluid to the destination when the firstvolume exceeds the second volume by a fraction, which may be apredetermined fraction, of the first incremental volume, and resumesdelivery of the first volume of fluid to the destination. The systemalso includes a valve arrangement for controlling fluid communicationbetween the destination and first and second fluid sources and acontroller for determining the first and second volumes of fluid, thefirst incremental volume of fluid, and for controlling the valvearrangement and the fluid control module.

[0013] In accordance with related embodiments, the first incrementalvolume may be less than one quarter of the target volume. Additionally,the desired ratio may be 1:1 and the predetermined fraction may beapproximately one half. In accordance with yet further relatedembodiments, the fluid control module may deliver the first and secondvolumes of fluid to a human subject, and the fluid control module maydeliver the first and second volumes of fluid parenterally. Similarly,the fluid control module may deliver the first and second volumes offluid to a fluid reservoir and/or to a container. Such a container maybe a heating bag and/or a pump chamber. The controller may alsodetermine that approximately the target volume minus a finish volume offluid has been delivered to the destination. Further, the fluid controlmodule may measure the volume of fluid delivered to the destination fromthe first source and the volume of fluid delivered to the destinationfrom the second source and deliver a third volume of fluid from thesource that has delivered a smaller volume of fluid to the destination.The third volume of fluid may be delivered in increments each havingapproximately a second incremental volume. The second incremental volumemay be less than the first incremental volume, such that the volume offluid delivered to the destination from the first source and the volumeof fluid delivered from the second source are in approximately thedesired ratio. Further, the sum of the first and the second volumes maybe approximately equal to the target volume minus a finish volume andthe second incremental volume may be less than the finish volume. Forexample, the second incremental volume may be less than one third thefinish volume.

[0014] In accordance with a further embodiment of the invention, asystem for delivering a target volume of fluid to a destination includesfluid delivery means for delivering a first volume of fluid to thedestination in one or more first incremental volumes, the first volumeof fluid being less than the target volume, and delivering a secondvolume of fluid to the destination in one or more second incrementalvolumes, the second incremental volume being less than the firstincremental volume. The system also includes measuring means formeasuring the volume of fluid delivered to the destination and controlmeans for controlling the fluid delivery means.

[0015] In accordance with another embodiment of the invention, a systemfor simultaneously delivering a target volume of fluid from two sourcesin a desired ratio to a common destination includes a first fluid sourceand a second fluid source. Fluid delivery means delivers a first volumeof fluid from the first fluid source and a second volume of fluid fromthe second fluid source to the destination in one or more firstincremental volumes, the first incremental volume being substantiallyless than the target volume. Measuring means measures the volume offluid delivered to the destination from the first source and the volumeof fluid delivered to the destination from the second source. Controlmeans suspends delivery of the first volume of fluid to the destinationwhen the first volume exceeds the desired ratio with respect to thesecond volume by a fraction, which may be a predetermined fraction, ofthe first incremental volume and then resumes delivery of the firstvolume of fluid to the destination.

[0016] In accordance with a further embodiment of the invention, asystem for simultaneously delivering a target volume of fluid from twosources in a desired ratio to a common destination includes a firstfluid source and a second fluid source. The system also includes fluiddelivery means for delivering a first volume of fluid from the firstfluid source and a second volume of fluid from the second fluid sourceto the destination in one or more first incremental volumes, the firstincremental volume being substantially less than the target volume, andmeasuring means for measuring the volume of fluid delivered to thedestination from the first source and the volume of fluid delivered tothe destination from the second source. The control means suspendsdelivery of the first volume of fluid to the destination when the firstvolume exceeds the second volume by a fraction, which may be apredetermined fraction, of the first incremental volume and resumesdelivery of the first volume of fluid to the destination. In accordancewith related embodiments, the desired ratio may be 1:1 and thepredetermined fraction may be approximately one half.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing features of the invention will be more readilyunderstood by reference to the following detailed description, takenwith reference to the accompanying drawings, in which:

[0018]FIG. 1 is a perspective view of an automated fluid delivery systemthat may be used in conjunction with the present invention;

[0019]FIG. 2 is a flow chart illustrating a method for delivering atarget volume of fluid to a destination in accordance with an embodimentof the invention;

[0020]FIG. 3 is a flow chart illustrating a method for simultaneouslydelivering a target volume of fluid from two sources in a desired ratioto a common destination in accordance with another embodiment of theinvention;

[0021]FIG. 4 is a flow chart illustrating a method for simultaneouslydelivering a target volume of fluid from two sources in a desired ratioto a common destination in accordance with yet another embodiment of theinvention; and

[0022]FIG. 5 is a block diagram illustrating one example of a system foremploying the methods of FIGS. 3 and 4.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0023]FIG. 1 is a perspective view of an automated fluid managementsystem that may be used in conjunction with the present invention. Thesystem 100 includes a liquid supply and delivery set 102, a fluidcontrol module 104 that interacts with the delivery set 102 to pumpliquid through it, and a controller 106 that governs the interaction toperform a selected procedure. In the depicted embodiment, the fluidcontrol module and controller are located within a common housing 182.

[0024] The fluid control module 104 utilizes a pneumatic pumping actionto emulate gravity flow, regardless of the position of the sourcesolution bags 184. The pumping action may be the result of pressurizingone or more fluid chambers through use of a control gas or liquid, orother methods known in the art, such as pumps, pistons, piezoelectricmechanisms, pressurized reservoirs, valves, clamps and vents. As notedabove, these pressurizing devices are explained in greater detail in thepatents referenced above and incorporated herein by reference.

[0025] The controller 106 carries out process control and monitoringfunctions for the fluid control module 104. The controller includes auser interface 167 with a display screen 137 and control pad. Theinterface 167 presents menus, sub-menus and status information to theuser during a therapy session. The interface 167 also allows the user toenter and edit therapy parameters, and to issue therapy commands. In oneembodiment, the user interface 167 receives characters from a keypad,displays text to the display screen 137 and sounds an alarm whenappropriate. The control pad may include a “Go” key 135, which whenpressed causes the interface 167 to display a main menu on the displayscreen 137 for initiating a therapy session, and a “Stop” key 139 whichwhen pressed causes a therapy session to cease. The interface 167 mayalso include keys 133 for traversing through the information and menusdisplayed on the display screen 137 and an “Enter” key 134 for causingdata to be input to the system or for selecting an entry from the menus.

[0026] In the illustrated embodiment, the controller 106 comprises acentral processing unit. The central processing unit may employconventional real time multi-tasking to allocate tasks. The centralprocessing unit may itself be programmable or alternatively, it may rununder the direction of a software, middle-ware or hardware programexternal to the system.

[0027] In use, for example as a peritoneal dialysis system, the userconnects the set 102 to his/her indwelling peritoneal catheter 108. Theuser also connects the set 102 to individual bags 184 containingperitoneal dialysis solution for infusion. The set 102 also connects toa heating bag 180 in which the dialysis solution is heated to a desiredtemperature. In accordance with an embodiment of the invention describedin more detail below, two or more fluids from different sources may besimultaneously pumped to the heating bag in a desired ratio.

[0028] The controller 106 paces the fluid control module 104 through aprescribed series of fill, dwell, and drain phases typical of anautomated peritoneal dialysis procedure. During the fill phase, thefluid control module 104 infuses the heated solution through the set 102and into the patient's peritoneal cavity. Following the dwell phase, thefluid control module 104 institutes a drain phase, during which thefluid control module 104 discharges spent dialysis solution from thepatient's peritoneal cavity through the set into a nearby drain.

[0029] The delivery set 102 includes a cassette (not visible) whichmounts inside a holder in the fluid control module 104. The cassetteserves in association with the fluid control module 104 and thecontroller to direct liquid flow among multiple fluid sources anddestinations that an automatic peritoneal dialysis procedure requires.The cassette forms an array of interior cavities in the shapes of wellsand channels. The interior cavities create one or more pump chambers andone or more paths to convey fluid. The interior cavities also create oneor more valve stations to interconnect the fluid paths with the pumpchambers and with each other. The number and arrangement of pumpchambers, liquid paths and valve stations can vary. Such a cassette isdescribed in U.S. Pat. No. 5,989,423 and U.S. Pat. No. 5,178,182 both ofwhich, as noted above, are incorporated herein by reference.

[0030] In order to accommodate patients with small abdominal cavities, anew process and system is presented that limits the available fillvolume. A clinician will be able to select a “low fill mode” from amongthe modes available on the fluid delivery system. For example, when thelow fill mode is on, the fill volumes available will be limited to arange of 60-1000 mL.

[0031] Since the fill volumes for the low-fill mode may be as small as60 mL, it is necessary to achieve a high level of targeting accuracy forthese applications. An acceptable range of accuracy may be, for example,+5 mL/−10 mL. It may also be desirable that conforming to this accuracyspecification does not take substantially longer than a standard fill.

[0032] The targeting accuracy is improved by executing a moreintermittent fill during the last phase, in which the incoming flow isstopped one or more times to perform a volume measurement and assessprogress. The nominal operation of this fill routine does not result infills that consistently stop at the low end of the tolerance; insteadthe nominal operation should fill to the mid-point of the tolerancerange. This fill routine especially improves performance for low-fillapplications.

[0033]FIG. 2 illustrates a method (i.e., a fill routine) for deliveringa target volume of fluid to a destination in accordance with oneembodiment of the invention. Such a destination may be a human subject,the heating bag 180, a reservoir, a fluid container or pump chamber asillustrated with respect to FIG. 5. The fluid may further be deliveredto the human subject parenterally. The method includes delivering 201 afirst volume of fluid to the destination in increments each havingapproximately a first incremental volume. The first volume of fluid isless than the target volume by an amount at least as large as the firstincremental volume. For example, if the target volume is 500 mL, thefirst incremental volume may be 10 to 50 mL. A second volume of fluid isthen delivered 202 to the destination in increments each havingapproximately a second incremental volume. The second incremental volumeis less than the first incremental volume, and the sum of the firstvolume and the second volume is approximately equal to the targetvolume. For example, if the first incremental volume is 15 mL, then thesecond incremental volume may be 1 to 3 mL. Note that a plurality offirst incremental volumes may be delivered before delivering the secondvolume. Thus, to achieve a target volume of 500 mL, the first volume maybe approximately 485 mL, delivered in thirty or more first incrementalvolumes of approximately 15 mL each, before the second volume of fluidis delivered in the second incremental volumes of approximately 1 to 3mL each. Thus, the first volume may approximately equal the targetvolume minus a finish volume (i.e., the second volumes) and the secondincremental volume may be less than the finish volume. For example, thesecond incremental volume may be one third the finish volume

[0034]FIG. 3 is a flow chart illustrating a method for simultaneouslydelivering a target volume of fluid from two sources in a desiredration, in this case in a 1:1 ratio, to a common destination. Again,such a destination may be a human subject, the heating bag 180, areservoir, a fluid container or pump chamber. Further, the fluid may bedelivered to a human subject parenterally. In a first step, a firstvolume of fluid from a first source and a second volume of fluid fromsecond source is delivered 301 to the destination in increments eachhaving approximately a first incremental volume. The first volume may bemeasured in one or more of the pump chambers discussed above inconnection with the fluid delivery system of FIG. 1 and in connectionwith the system FIG. 5. In one embodiment, for example, the volumemeasurement systems of U.S. Pat. Nos. 4,976,162 and 4,826,482(incorporated herein above) are employed. The first incremental volumeof fluid is substantially less than the target volume. In oneembodiment, the first incremental volume is less than one quarter of thetarget volume. However, the first incremental volume may be less thanthe target volume by any desired fraction, such as one eighth, onethird, one half, two thirds, etc.

[0035] After delivery of a first incremental volume of fluid from eachof the first source and the second source, the volume of fluid deliveredto the destination from the first source and the volume of fluiddelivered to the destination from the second source is measured 302.Such delivery may occur simultaneously and such measurements may beperformed by the controller 106 by using pressure transducers containedin the fluid control module 104 or other fluid volume measuringapparatuses. Delivery of the first volume of fluid to the destination issuspended 303 when the first volume exceeds the second volume by afraction, which may be a predetermined fraction, of the firstincremental volume. For example, delivery of the first volume of fluidto the destination may be suspended when the first volume exceeds thesecond volume by approximately one half of the first incremental volumein order to attain a 1:1 one ratio. A first incremental volume of fluidis then delivered 304 to the destination from the second source, anddelivery of the first volume of fluid to the destination is resumed 305.It will be appreciated that this process may be adapted for a desiredratio other than one-to-one. In such a case, the fluids from differentsources may be delivered by incremental volumes that are the same orthat are different from each other. It will also be appreciated thatthis process may be adapted for use with fluids from more than twodifferent sources.

[0036]FIG. 4 is a flow chart illustrating a method for simultaneouslydelivering a target volume of fluid from two sources in a desired (suchas a one-to-one) ratio to a common destination in accordance with yetanother embodiment of the invention. The procedure begins in a mannersimilar to that shown with respect to the embodiment of FIG. 3. That is,a first volume of fluid from a first source and a second volume of fluidfrom second source is delivered 401 to the destination in incrementseach having approximately a first incremental volume. The firstincremental volume of fluid is less than the target volume. In this casethe first incremental volume is less than one quarter of the targetvolume. However, as noted above the first incremental volume may be lessthan the target volume by any desired ratio. After delivery of a firstincremental volume of fluid from each of the first source and the secondsource, the volume of fluid delivered to the destination from the firstsource and the volume of fluid delivered to the destination from thesecond source is measured 402. Again, such measurements may be performedby the controller 106 by using pressure transducers contained in thefluid control module 104 or other fluid volume measuring means. Deliveryof the first volume of fluid to the destination is suspended 403 whenthe first volume exceeds the second volume by a fraction, which may be apredetermined fraction, of the first incremental volume, in this case byone half the first incremental volume. A first incremental volume offluid is then delivered 404 to the destination from the second source,and delivery of the first volume of fluid to the destination is resumed405.

[0037] In order to assure that the target volume is delivered in thedesired ratio, a determination is made 406 when approximately the targetvolume of fluid has been delivered to the destination. The volume offluid delivered to the destination from the first source and the volumeof fluid delivered to the destination from the second source are thenmeasured 407. Following this measurement, a third volume of fluid fromthe source that has delivered a smaller volume of fluid to thedestination is delivered 408 in increments each having approximately asecond incremental volume. The second incremental volume is less thanthe first incremental volume. As a result of delivering the third volumeof fluid, the sum of the volume of fluid delivered to the destinationfrom the first source and the volume of fluid delivered from the secondsource are in approximately the desired ratio, in this case a one to oneratio. The first volume and the second volume may each be approximatelyequal to the target volume minus a finish volume. Similarly, the secondincremental volume may be less than the finish volume by any desiredfraction. For example, in this embodiment, the second incremental volumemay be one third the finish volume.

[0038] A system similar to the one described with respect to FIG. 1 mayincorporate the processes described above. In this case the fluidcontrol module 104 or other fluid delivery means such as those disclosedin the patents incorporated above, delivers a first volume of fluid tothe destination in increments each having approximately a firstincremental volume, the first volume of fluid being less than the targetvolume. The fluid control module 104 will also deliver a second volumeof fluid to the destination in increments each having approximately asecond incremental volume. Here again, the second incremental volume isless than the first incremental volume, such that the sum of the firstvolume and the second volume is approximately equal to the targetvolume. The system additionally includes a valve arrangement, showngenerally at 105 for controlling fluid communication between the fluidsource or sources and the destination as well as a controller, such ascontroller 106 or other control means such as a microprocessor orcomputer. The controller 106 determines the volume of fluid delivered tothe destination and for controls the valve arrangement 105 and the fluidcontrol module 104. The controller 106 may also determine whenapproximately the target volume minus a finish volume of fluid hasdelivered to the destination. In addition, the fluid control module 104may measure the volume of fluid delivered to the destination from thefirst source and the volume of fluid delivered to the destination fromthe second source. The fluid control module 104 may then deliver a thirdvolume of fluid from the source that has delivered a smaller volume offluid to the destination in increments each having approximately asecond incremental volume.

[0039]FIG. 5 is a block diagram illustrating an example of a system foremploying the methods of FIGS. 3 and 4 above. The system includes afirst fluid source 501 and a second fluid source 502. The first fluidsource 501 is in fluid communication with a first pump chamber 507 viavalve 503 and the second fluid source 502 is in fluid communication witha second pump chamber 510 via valve 505. Pump chamber 507 is also incommunication with a volume measurement system 508 and pump chamber 510is in communication with volume measurement system 509. Alternatively,each pump chamber 507 and 510 may be in communication with a commonvolume measurement system. Each of the pump chambers 501 and 502 mayinclude flexible membranes as described in the above referenced andincorporated patents. Similarly, each of the volume measurement systems508 and 509 may include pressure transducers and positive and/ornegative pressure reservoirs as are also described in the aforementionedincorporated patents. Each of the pump chambers 507 and 510 is in fluidcommunication with a destination 511 via valves 504 and 506respectively. As noted above, the destination 511 may be a humansubject, a reservoir, a container, such as a heating bag, or another,perhaps larger, pump chamber.

[0040] In accordance with one embodiment, the goal is to separatelytrack the volumes moved from each fluid source 501 and 502 and to ensurethat the difference between the fluid delivered from each of the twofluid sources never varies by more than half the volume of a pumpchamber. This is achieved by performing in-phase pumping such that bothpump chambers 507 and 510 fill and deliver in sync. For example, if eachpump chamber holds 15 mL, and it is determined that one pump chamber,for example pump chamber 507, has delivered at least 7.5 mL more fluidto the destination 511 than the other pump chamber 510, then fluiddelivery from pump chamber 507 will be suspended while pump chamber 510performs a catch-up stroke. Such a determination is made by measuringthe fluid volumes of each pump chamber 507 and 510 for each pumpingstroke via volume measurement systems 508 and 509 respectively. (Itshould be noted that while each pump chamber 507 and 510 may have acapacity of 15 mL, somewhat less than 15 mL of fluid may be delivered toand by each pump chamber during any single pumping stroke.) When thetarget volume (the volume of fluid intended to be delivered to thedestination) has been delivered to the destination 511, the pumpchamber, perhaps pump chamber 510, that has delivered the most fluid tothe destination 511 will stop pumping. The pump chamber which hasdelivered the least amount of fluid, in this case pump chamber 507, willthen switch to a “targeting mode” in which a maximum of 3 mL of fluid isdelivered to the destination 511 per pump chamber stroke. This targetingmode insures that a 1:1 ratio (or other desired ratio) between fluiddelivered to the destination 511 from the first fluid source 501 andfluid delivered to the destination 511 from the second fluid source 502is achieved to within approximately plus 2 mL or minus 1 mL.

[0041] While the invention has been described in connection withspecific embodiments thereof, it will be understood that it is capableof further modification. This application is intended to cover anyvariation, uses, or adaptations of the invention and including suchdepartures from the present disclosure as come within known or customarypractice in the art to which the invention pertains.

What is claimed is:
 1. A method for delivering a target volume of fluidto a destination, the method comprising: delivering a first volume offluid to the destination in increments each having approximately a firstincremental volume, the first volume of fluid being less than the targetvolume; and delivering a second volume of fluid to the destination inincrements each having approximately a second incremental volume, thesecond incremental volume being less than the first incremental volume,such that the sum of the first volume and the second volume isapproximately equal to the target volume.
 2. A method according to claim1, wherein delivering the first and second volumes of fluid to adestination includes delivering the first and second volumes of fluidparenterally to a human subject.
 3. A method according to claim 1wherein the first volume is approximately equal to the target volumeminus a finish volume.
 4. A method according to claim 3, wherein thesecond incremental volume is less than the finish volume.
 5. A methodaccording to claim 3, wherein the second incremental volume is less thanone third the finish volume.
 6. A method according to claim 1, whereindelivering the first volume and second volumes of fluid to a destinationincludes delivering the first and second volumes of fluid to a fluidreservoir.
 7. A method according to claim 1, wherein delivering thefirst and second volumes of fluid to a destination includes deliveringthe first and second volumes of fluid to container.
 8. A methodaccording to claim 7, wherein the container is a heating bag.
 9. Amethod according to claim 7, wherein the container is a pump chamber.10. A system for delivering a target volume of fluid to a destinationcomprising: a fluid control module for delivering a first volume offluid to the destination in increments each having approximately a firstincremental volume, the first volume of fluid being less than the targetvolume, and delivering a second volume of fluid to the destination inincrements each having approximately a second incremental volume, thesecond incremental volume being less than the first incremental volume,such that the sum of the first volume and the second volume isapproximately equal to the target volume; a valve arrangement forcontrolling fluid communication to the destination; and a controller fordetermining the volume of fluid delivered to the destination and forcontrolling the valve arrangement and the fluid control module.
 11. Asystem according to claim 10, wherein the fluid control module deliversthe first and second volumes of fluid to a human subject.
 12. A systemaccording to claim 11, wherein the fluid control module delivers thefirst and second volumes of fluid parenterally.
 13. A system accordingto claim 10, wherein the fluid control module delivers the first andsecond volumes of fluid to a fluid reservoir.
 14. A system according toclaim 10, wherein the fluid control module delivers the first and secondvolumes of fluid to a container.
 15. A system according to claim 14,wherein the container is a heating bag.
 16. A system according to claim14, wherein the container is a pump chamber.
 17. A system according toclaim 10, wherein the first volume is approximately equal to the targetvolume minus a finish volume.
 18. A system according to claim 17,wherein the second incremental volume is less than the finish volume.19. A system according to claim 17, wherein the second incrementalvolume is less than one third the finish value.
 20. A method forsimultaneously delivering a target volume of fluid from two sources in adesired ratio to a common destination, the method comprising: deliveringa first volume of fluid from a first source and a second volume of fluidfrom a second source to the destination in increments each havingapproximately a first incremental volume, the first incremental volumeof fluid being substantially less than the target volume; after deliveryof a first incremental volume of fluid from the first source and thesecond source, measuring the volume of fluid delivered to thedestination from the first source and the volume of fluid delivered tothe destination from the second source; suspending delivery of the firstvolume of fluid to the destination when the first volume exceeds thesecond volume by a predetermined fraction of the first incrementalvolume; delivering a first incremental volume of fluid from the secondsource; and resuming delivery of the first volume of fluid to thedestination.
 21. A method according to claim 20, wherein the firstincremental value is less than one quarter of the target value.
 22. Amethod according to claim 20, wherein the desired ration is 1:1.
 23. Amethod according to claim 22, wherein the predetermined fraction is onehalf.
 24. A method according to claim 20, wherein delivering the firstand second volumes of fluid to a destination includes delivering thefirst and second volumes of fluid parenterally to a human subject.
 25. Amethod according to claim 20, wherein delivering the first volume andsecond volumes of fluid to a destination includes delivering the firstand second volumes of fluid to a fluid reservoir.
 26. A method accordingto claim 20, wherein delivering the first and second volumes of fluid toa destination includes delivering the first and second volumes of fluidto container.
 27. A method according to claim 26, wherein the containeris a heating bag.
 28. A method according to claim 26, wherein thecontainer is a pump chamber.
 29. A method according to claim 20, furthercomprising: determining that approximately the target volume of fluidhas been delivered to the destination; measuring the volume of fluiddelivered to the destination from the first source and the volume offluid delivered to the destination from the second source; anddelivering a third volume of fluid from the source that has delivered asmaller volume of fluid to the destination in increments each havingapproximately a second incremental volume, the second incremental volumebeing less than the first incremental volume, such that the volume offluid delivered to the destination from the first source and the volumeof fluid delivered from the second source are in approximately thedesired ratio.
 30. A method according to claim 29, wherein the sum ofthe first volume and the second volume is approximately equal to thetarget volume minus a finish volume.
 31. A method according to claim 30,wherein the second incremental volume is less than the finish volume.32. A method according to claim 30, wherein the second incrementalvolume is less than one third the finish volume.
 33. A system forsimultaneously delivering a target volume of fluid from two sources in adesired ratio to a common destination, the system comprising: a firstfluid source; a second fluid source; a fluid control module for:delivering a first volume of fluid from the first fluid source and asecond volume of fluid from the second fluid source to the destinationin increments each having approximately a first incremental volume, thefirst incremental volume being substantially less than the targetvolume, measuring the volume of fluid delivered to the destination fromthe first source and the volume of fluid delivered to the destinationfrom the second source, suspending delivery of the first volume of fluidto the destination when the first volume exceeds the second volume by apredetermined fraction of the first incremental volume, and resumingdelivery of the first volume of fluid to the destination; a valvearrangement for controlling fluid communication between the destinationand first and second fluid sources; and a controller for determining thefirst and second volumes of fluid, the first incremental volume offluid, and for controlling the valve arrangement and the fluid controlmodule.
 34. A system according to claim 33, wherein the firstincremental volume is less than one quarter of the target volume.
 35. Asystem according to claim 33, wherein the desired ratio is 1:1.
 36. Asystem according to claim 35, wherein the predetermined fraction isapproximately one half.
 37. A system according to claim 33, wherein thefluid control module delivers the first and second volumes of fluid to ahuman subject.
 38. A system according to claim 37, wherein the fluidcontrol module delivers the first and second volumes of fluidparenterally.
 39. A system according to claim 33, wherein the fluidcontrol module delivers the first and second volumes of fluid to a fluidreservoir.
 40. A system according to claim 33, wherein the fluid controlmodule delivers the first and second volumes of fluid to a container.41. A system according to claim 40, wherein the container is a heatingbag.
 42. A system according to claim 40, wherein the container is a pumpchamber.
 43. A system according to claim 33, wherein the controllerfurther determines that approximately the target volume minus a finishvolume of fluid has been delivered to the destination; and the fluidcontrol module further: measures the volume of fluid delivered to thedestination from the first source and the volume of fluid delivered tothe destination from the second source; and delivers a third volume offluid from the source that has delivered a smaller volume of fluid tothe destination in increments each having approximately a secondincremental volume, wherein the second incremental volume is less thanthe first incremental volume, such that the volume of fluid delivered tothe destination from the first source and the volume of fluid deliveredfrom the second source are in approximately the desired ratio.
 44. Asystem according to claim 43, wherein the sum of the first volume andthe second volume is approximately equal to the target volume minus afinish volume.
 45. A system according to claim 44, wherein the secondincremental volume is less than the finish volume.
 46. A systemaccording to claim 44, wherein the second incremental volume is lessthan one third the finish volume.
 47. A system for delivering a targetvolume of fluid to a destination comprising: fluid delivery means fordelivering a first volume of fluid to the destination in one or morefirst incremental volumes, the first volume of fluid being less than thetarget volume, and delivering a second volume of fluid to thedestination in one or more second incremental volumes, the secondincremental volume being less than the first incremental volume;measuring means for measuring the volume of fluid delivered to thedestination; and control means for controlling the fluid delivery means.48. A system for simultaneously delivering a target volume of fluid fromtwo sources in a desired ratio to a common destination, the methodcomprising: a first fluid source; a second fluid source; fluid deliverymeans for delivering a first volume of fluid from the first fluid sourceand a second volume of fluid from the second fluid source to thedestination in one or more first incremental volumes, the firstincremental volume being substantially less than the target volume;measuring means for measuring the volume of fluid delivered to thedestination from the first source and the volume of fluid delivered tothe destination from the second source; and control means for suspendingdelivery of the first volume of fluid to the destination when the firstvolume exceeds the desired ratio with respect to the second volume by afraction of the first incremental volume and resuming delivery of thefirst volume of fluid to the destination.
 49. A system forsimultaneously delivering a target volume of fluid from two sources in adesired ratio to a common destination, the system comprising: a firstfluid source; a second fluid source; fluid delivery means for deliveringa first volume of fluid from the first fluid source and a second volumeof fluid from the second fluid source to the destination in one or morefirst incremental volumes, the first incremental volume beingsubstantially less than the target volume; measuring means for measuringthe volume of fluid delivered to the destination from the first sourceand the volume of fluid delivered to the destination from the secondsource; and control means for suspending delivery of the first volume offluid to the destination when the first volume exceeds the second volumeby a predetermined fraction of the first incremental volume and resumingdelivery of the first volume of fluid to the destination.
 50. A systemaccording to claim 49, wherein the desired ratio is 1:1.
 51. A systemaccording to claim 50, wherein the predetermined fraction isapproximately one half.